since you can't see the animations now check the "timecourse" box, now

the fishes are green, light green meaning: ready to produce a child, dark green for those who just had a birth and all shades inbetween for pregnancy

the sharks are red, light red meaning: "I just had a tasty meal" and dark red for "I will starve next turn" and -again- all shades inbetween

Finally change the three numerical values - maybe you increase fish pregnancy to 20 or even 30 and reduce the sharks pregnancy time? (Increase grid size to 150x150 to prevent extinction of one species)